[Cmd + Shift + 4] Press and hold 'Command' & 'Shift' key and press 4 to select an area on the screen.
Tip: You can even press spacebar instead of clicking -> Then click on any window and that will be saved

[Cmd + Shift + Ctrl + 4] Press and hold 'Command' & 'Shift' & 'Ctrl' key and press 4 to select an area on the screen and copy to the clipboard.
Tip: You can even press spacebar instead of clicking -> Then click on any window and that will be copied.